The effect of sodium bicarbonate (alkalinity stress) on growth, and physiological and nutritional characteristics in three leafy vegetables (lettuce, amaranth and water convolvulus) were evaluated. In order to study the deleterious effect of alkalinity stress on plants, a factorial experiment was conducted with two factors including plant with three species and sodium bicarbonate in three levels (0, 5 and 10 mM) with three replicates. Data analysis was performed in a completely randomized design. Seedlings, after transplanting into the hydroponic condition, were put under stress for one month. According to the obtained results, shoot and root dry mass showed reduction with increase of sodium bicarbonate concentration. In response to elevated sodium bicarbonate concentrations; the plant pigments, maximum quantum yield (F_v/F_m) and photosynthetic performance index (PI) decreased in all examined plant species, however the lowest decrease, were observed in water convolvulus. The highest accumulation of proline and soluble carbohydrates was observed in water convolvulus with 10 mM sodium bicarbonate, so that soluble carbohydrates in water convolvulus at 10 mM increased 227% compared to control. Increase of sodium bicarbonate concentrations leaded to decrease in K, Fe and Zn and increase in Na in shoots and roots of plants. The results showed that water convolvulus was the most tolerance species to sodium bicarbonate among the studied plants.